The invention relates to fluid flow control valves. The invention relates more particularly to a fluid flow control valve having an orifice defining a seat against which an elastomeric diaphragm is urged by pressure differential occurring across the diaphragm such that fluid flows through flow control passages defined between the diaphragm and the seat, and in which increasing pressure differential across the diaphragm causes the diaphragm to constrict the flow control passages through deflection of the diaphragm.
Fluid flow control valves of the above-described type are particularly used for regulating fluid flow to a substantially constant flow rate over a range of pressure differentials, such as about 0.1 bar to 10 bars. In such valves, the diaphragm typically comprises a solid body of elastomeric material. When urged against the seat of the orifice, the diaphragm deforms, the degree of deformation increasing with increasing pressure differential across the diaphragm. As the deformation of the diaphragm increases, the flow control passages between the diaphragm and the seat become smaller. The valve is designed such that over the range of pressure differentials of interest, the changing flow area of the flow control passages offsets the changing pressure differential so as to maintain the flow rate substantially constant.
A common type of flow control valve employs a xe2x80x9ctorpedoxe2x80x9d shaped diaphragm that has an outer peripheral surface of smaller diameter than the inner surface of the housing of the valve. In normal forward flow through the valve, fluid flows between the outer peripheral surface of the diaphragm and the inner surface of the housing and then is turned radially inwardly by the orifice and flows through the flow control passages between an end face of the diaphragm and the orifice seat.
The flow rate through the flow control passages is proportional to the flow area of the passages multiplied by the square root of the pressure. Accordingly, the flow area of the flow control passages must change significantly from the lowest working pressure to the highest working pressure (e.g., from 0.1 bar to 10 bars) in order to maintain the flow rate substantially constant at all pressures. Various approaches have been taken to try to tailor the deflection of the diaphragm against the orifice seat so as to maintain approximately constant flow rate over the working pressure range. One prior approach employed a plurality of small projections of very small contact area on the orifice surface that engage the diaphragm in an attempt to increase the flow area at the low end of the pressure range. At low pressure differential, as the pressure differential increases the projections press into the diaphragm and locally deform it and the face of the diaphragm moves closer to the main surface of the orifice seat. A drawback of this approach is that the very small contact area of the projections causes a significant hysteresis effect. The valve also tends to have higher than desired flow in the pressure range where the diaphragm deflection makes a transition from local deformation to bending.
Another prior approach was to limit the deflection of the diaphragm to pure compression without bending, as shown in U.S. Pat. No. 3,189,125. This was accomplished by making the diaphragm of sufficient thickness and shaping the diaphragm to have its thickest section at the center so that substantially no bending would occur. This approach works well for differential pressures exceeding 1.0 bar. However, when the operating rang,e is expanded to include pressure differentials below 1.0 bar, problems begin to arise.
Other prior devices have employed annular washer-type diaphragms that bend as the pressure differential increases, thus changing the flow area through the center of the diaphragm, as shown in U.S. Pat. No. 4,986,312. These devices are prone to excessive bending-beam creeping and, thus, inaccuracy over time.
Another disadvantage of many prior flow control valves is that during reverse flow through the valve, such as when backflushing a fluid system, the valve may not allow fluid to freely pass in the reverse direction, and the diaphragm in some valves may even become dislodged from its proper position.
The present invention provides a fluid flow control valve comprising a housing defining a fluid flow passage extending therethrough, the housing having opposite ends each defining an opening for flow into and out of the fluid flow passage, and an orifice and diaphragm disposed in the housing. The orifice has a seat at one end thereof. The diaphragm has one end face that opposes the scat of the orifice, the seat being configured such that one or more flow control passages are defined between the seat and the one end face of the diaphragm through which the fluid flows. In accordance with the invention, the seat is contoured to include at least two different shapes of channels each promoting localized bending of the diaphragm at a different pressure differential, thereby permitting an expansion of the working pressure range to very low pressure differentials. The localized bending of the diaphragm can be modeled as a simple supported beam bending, which is well understood and readily predicted, thus making the prediction of the diaphragm movement more accurate than prediction of complex diaphragm deflections that occur in many prior flow control valves. Accordingly, the accuracy of the flow control valve can be improved over that of prior valves having complex diaphragm deflection modes.
In accordance with a preferred embodiment of the invention, the seat of the orifice has a main support surface defining a plurality of channels therein including at least one relatively wide channel promoting localized bending of the diaphragm thereinto at a relatively low pressure differential range, and at least one relatively narrow channel promoting localized bending of the diaphragm thereinto at a relatively higher pressure differential range, each channel extending in a transverse direction of the orifice and the channels being circumferentially spaced from each other.
The channels preferably have a V-shaped cross section normal to the transverse direction. The walls defining the channel can be planar or non-planar. One or more of the channels can include a longitudinal slot formed at the bottom of the channel. The slot preferably is engaged by and begins to be constricted by the diaphragm after the channel has been completely closed off by the diaphragm. The slot thus functions as a third type of channel regulating flow rate at a third range of pressure differentials higher than that of the wide and narrow converging channels.
In accordance with another preferred embodiment of the invention, the orifice includes a plurality of spaced protrusions that extend beyond the main support surface in the direction toward the diaphragm. The protrusions engage the diaphragm and hold it off the main support surface at low pressure differentials. The protrusions preferably are sized in contact area and are spaced in relation to the diaphragm so as to promote bending of the diaphragm between the protrusions. Between each two adjacent protrusions there preferably is at least one of the channels. Thus, at low pressure differentials, the diaphragm bends between the protrusions, eventually coming into contact with the main support surface on either side of the channel(s) as the pressure differential increases to a predetermined magnitude. Further increases in the pressure differential then cause the diaphragm to bend into the channel(s). Each channel will be completely closed off by the diaphragm when the pressure differential becomes large enough, the wide channels becoming closed at a lower pressure differential than the narrow channels. The diaphragm preferably has sufficient rigidity, through careful selection of its length-to-diameter ratio and durometer hardness, to permit the localized bending of the diaphragm into the channels while substantially reducing the creep of the diaphragm over time. Preferably, the diaphragm has a length-to-diameter ratio from about 0.1:1 to about 0.47: 1, and a Shore A durometer hardness from about 55 to about 69.
In a preferred arrangement of the channels, there are at least two of the relatively wide channels located immediately adjacent each other so as to define therebetween a diaphragm-engaging surface of inverted V-shaped cross section tapering toward the diaphragm. Still more preferably, there are four of the relatively wide channels arranged in two pairs, the channels of each pair being immediately adjacent each other so as to define therebetween a diaphragm-engaging surface of inverted V-shaped cross section tapering toward the diaphragm. The two diaphragm-engaging surfaces of inverted V-shaped cross section preferably are on diametrically opposite sides of the longitudinal axis of the orifice. The four protrusions preferably are arranged in two pairs, the protrusions of each pair having one of the pairs of relatively wide channels located therebetween. The seat preferably includes two of the relatively narrow channels spaced about 90xc2x0 from the diaphragm-engaging surfaces of inverted V-shaped cross section. Each of the relatively narrow channels is defined in a portion of the main support surface that is normal to the longitudinal axis of the orifice.